The present invention relates to ultrasonic imaging systems for imaging an object for the detection of flaws, defects, internal inhomogeneities and the like.
Ultrasonic imaging is used widely for detection of flaws, defects, internal inhomogeneities and the like in an object, for example, a welded joint. In principle, ultrasonic imaging involves imaging the object using an ultrasonic probe for transmitting a train of ultrasound energy pulses toward the object and for receiving the echo pulses reflected by the object. Display of the flaws, defects, internal inhomogeneities and the like in the object is achieved through the detection of changes in the amplitude and/or the travel time of the echo pulses. Several techniques of ultrasonic imaging are known in the art including A-scan imaging on an oscilloscope, B-scan imaging, C-scan imaging and P-scan imaging as described in an article entitled "Objectivization of the results of ultrasonic inspection of welding seams" by Dr. G. S. Passi in the English-language version of the Soviet Journal of Non-destructive testing, Vol. 23, No. 6, June, 1987, pgs. 372-379.
A conventional ultrasound imaging system, generally designated 10, will now be described with reference to FIG. 1. Ultrasound imaging system 10 includes an ultrasonic probe 12 for transmitting pulses of ultrasonic energy toward an object 14 under test, for example, a welded joint, and for receiving echo pulses reflected therefrom. Ultrasonic probe 12 is typically a hand-held implement for manipulation by an operator. The operator grips ultrasonic probe 12 and applies its head to object 14. The operator manipulates ultrasonic probe 12 over object 14 according to a trajectory stipulated by the type of object, size of object and other parameters. The operator typically holds ultrasonic probe 12 at normal incidence with respect to object 14. When the surface of object 14 is inaccessible or irregular, for example, in the case, of the top bead of a weld, the operator is required to employ an angle ultrasonic probe.
The location of ultrasonic probe 12 on object 14 is determined by a probe location monitoring apparatus 16 providing real time feedback of the actual trajectory of ultrasonic probe 12 on object 14 to the operator. Probe location monitoring apparatus 16 typically includes an air acoustic emitter 18 for transmitting a signal and a receiver 20 for detecting the signal. Air acoustic emitter 18 is preferably integrated with ultrasonic probe 12 while receiver 20 is preferably in the form of two microphones 22 and 24 placed at a rightangle to one another for providing a Cartesian co-ordinate system. The degree of acoustic coupling between ultrasonic probe 12 and object 14 is determined by an acoustic coupling monitoring apparatus 26. Acoustic coupling monitoring apparatus 26 typically includes a low frequency noise vibrator 28 for transmitting a reference signal into object 14 for pick up by ultrasonic probe 12.
System 10 further includes digital computer apparatus 30 for generating a scan image of object 14 by correlating between the amplitude and/or time delays of echo pulses received by ultrasonic probe 12 and the location of ultrasonic probe 12 as provided by probe location monitoring apparatus 16. Hence, digital computer apparatus 30 includes a defect image array 32 for storing data regarding the flaws, defects and internal inhomogeneities, if any, detected in object 14 and a trajectory image array 34 for storing data regarding the actual trajectory of ultrasonic probe 12 with respect to object 14. Defects image array 32 displays the images of object 14 on an image display 36 which typically displays a "Top View" image 38 of object 14, a "Side View" image 40 of object 14 and an "End View" image 42 of object 14. For the sake of exposition, different views of a defect 44 in object 14 are shown in Top View image 38, Side View image 40 and End View image 42.
Digital computer apparatus 30 also displays the actual trajectory of ultrasonic probe 12 on the surface of object 14 on a trajectory display 46. The actual trajectory, generally designated 48, includes zones 50 where the acoustic coupling between ultrasonic probe 12 and object 14 is equal to or greater than a pre-determined threshold and zones 52 which suffer from an insufficient degree of acoustic coupling between ultrasonic probe 12 and object 14. For the sake of clarity, the equivalent of trajectory 48 has been represented by a partly broken trajectory on object 14.
It is well known that the images of flaws, defects, internal inhomogeneities and the like rendered by ultrasound imaging suffer from a number of deficiencies due to the manual manipulation of the probe. These deficiencies include the proficiency that an operator performs the scanning trajectory, the consistency of the acoustic coupling between the ultrasonic probe and the object under test as determined by the pressure applied by the operator, the angle that the operator holds the probe with respect to the object, and the like. Other deficiencies include that trajectory display 46 does not provide indication of which areas of the object have been scanned by ultrasonic probe 12 or the location of ultrasonic probe 12 with respect to object 14 when there is no acoustic coupling therebetween.
Turning now to FIG. 2, ultrasound imaging system 10 includes an angle ultrasonic probe 54 for imaging an object 14 when some or all of the portion of object 14 to be scanned is inaccessible. Angle ultrasonic probe 54 includes a scanning ultrasonic crystal 56 connected to digital computing apparatus 30 and an acoustic coupling ultrasonic crystal 58 connected to acoustic coupling monitoring apparatus designated 60 to distinguish it from acoustic coupling monitoring apparatus 26. In addition, system 10 employs a synchronizer 62 to ensure that there is no interference between the operation of scanning ultrasonic crystal 56 and acoustic coupling ultrasonic crystal 58. As can be clearly seen, scanning ultrasonic crystal 56 is inclined at an angle to object 14 while acoustic coupling ultrasonic crystal 58 is substantially normal to object 14. In this case, acoustic coupling monitoring apparatus 60 compares the level of the first backwall echo pulse from the backwall of object 14 to a threshold to determine zones 50 where the acoustic coupling between scanning ultrasonic probe 56 and object 14 is equal to or greater than the pre-determined threshold and zones 52 which suffer from an insufficient degree of acoustic coupling between scanning ultrasonic probe 56 and object 14. It is well known that acoustic coupling monitoring apparatus 60 suffers from low reliability due to the amplitude of backwall echo pulses depending not only on the state of the acoustic coupling but on other factors, for example, the local changing curvature of the tested objects, local non-parallelity of tested objects' surfaces, structural inhomogeneities in the tested objects, and the like. Furthermore, ultrasound imaging using an angle ultrasonic probe suffers from similar deficiencies as conventional probes due to the manual manipulation of the probe.
There is therefore a need for ultrasound imaging systems for imaging objects for the detection of flaws, defects, inherent inhomogeneities and the like in objects overcoming the deficiencies of conventional ultrasound imaging systems.